1. Field of the Invention
This invention relates generally to a video signal processing apparatus and more particularly, the invention relates to a video signal processing apparatus for reproducing color difference signals derived from a video signal wherein two color difference signals are transmitted line-sequentially, such as image processing apparatus of SECAM system and some image processing apparatus of MAC (Multiplexed Analogue Components) system for reproducing parallel color difference signals.
2. Description of the Prior Art
In the SECAM or the C, D, OR D.sub.2 type MAC system where two fundamental color difference signals (R-Y, B-Y) are transmitted line-sequentially, as shown in FIG. 4, color difference signals are reproduced through a time aligning process. The transmitted video signal is delayed by lH (horizontal scanning interval), then replacing the transmitted video singal with the delayed signal in response to a timing signal made from the video signal. FIG. 3 shows a prior art video signal processing apparatus of the SECAM system for reproducing color difference signals. FIG. 5 shows a prior art video signal processing apparatus of the MAC system for reproducing color difference signals. In FIGS. 3 and 5, numerals 10, 10' denote a timing signal generator; numeral 12, a delay circuit of lH; numeral 14, a delay circuit of 2H; numeral 41, an adder, numeral 20, a line switching circuit (hereinbelow also referred to as switching circuit). Reference "DL" shown in these Figures indicates a delay circuit.
In a video signal processing apparatus having the above-mentioned circuit arrangement for reproducing color difference signals, color blurring occurs at a horizontal color boundary of reproduced image where the hue changes greatly. The problem is due to a fact that two or three scanning lines are involved in the time aligning process to reproduce the color boundary. This problem will be further described with FIGS. 3 and 5.
FIG. 4 is a schematic illustration for illustrating the SECAM base band video signal signal applied to a video signal processing apparatus of the SECAM system. In FIG. 4, reference "U" shows color difference component "R-Y"; reference "V", color difference component "B-Y"; reference "n", the number of a scanning line. When the signal indicated by "n" is outputted, one line of the signal block "U.sub.n " is outputted as signal "R-Y"; the signal block "V.sub.n-1 " incoming one-scanning interval preceding to the signal block "U.sub.n " is outputted as "B-Y" signal. When a subsequent signal indicated as "n+1" is outputted, "Un" is outputted as signal "B-Y". If the hue largely changes from a moment between the line "n-1" and line "n" (indicated by "A" in FIG. 4), color around this point turns to smear, i.e., color blurring occurs at the corresponding the hue of the color of the line "n" is produced in the time aligning process from B-Y of the signal block "V.sub.n-1 " and R-Y of the signal block "U.sub.n " which are different each other as separated by the point "A".
FIG. 5 is a prior art video signal processing apparatus for reproducing color difference signals of the MAC system. FIG. 6 is a schematic illustration for illustrating the MAC system video signal inputted into a video signal processing apparatus of MAC system. When color signals of "n" line are processed, the signal block "U.sub.n " is outputted at the line switch circuit 20 as signal "R-Y"; a processed signal (V.sub.n-1 -V.sub.n+1)/2, as signal "B-Y". When color signals of the next line, i.e., of "n+1", a processed signal (U.sub.n +U.sub.n+1)/2 is outputted as "R-Y" signal; the signal block V.sub.n+1 is outputted. If a large change of hue occurs from a moment between lines "n-1" and "n" (indicated by "B" in FIG. 6) or occurs from a monent between lines "n" and "n+1" (indicated by "C"), signal contents of the signal blocks V.sub.n-1 and V.sub.n+1 largely differ each other. In this condition, signals "B-Y" and "R-Y" reproduced by the prior art reproducing circuit shown in FIG. 5 reproduces hue different from that of line "n-1" or former lines as well as different from line "n+1" or subsequent lines; thus, making a smeared hue, i.e., developing color blurring on the displayed image.
In the above-mentioned prior art video signal processing apparatus, even if "V" and "U" components were interchanged each other, the operation would be the same as the afore-mentioned operation, thus, color blurring would occur.
Accordingly, in the prior art video signal processing apparatus including the afore-mentioned prior art video signal processing apparatus, there is a drawback that color blurring develops when a large hue change between scanning lines occurs.